The invention relates to an apparatus for removing haze in a photo mask and a method for removing haze in a photo mask.
As semiconductor device become more highly integrated, the sizes of patterns formed on a wafer decrease accordingly. To form such fine patterns, a photolithography process using a photo mask is used. With the photolithography process, a photoresist layer is applied onto a material layer on which a desired pattern will be formed, and light is irradiated onto a part of the photoresist layer through a photo mask having a predetermined, light shielding pattern. Subsequently, the irradiated part of the photoresist layer is removed by a developing process using a developer solution, so as to form a photoresist layer pattern. Thereafter, the photoresist layer pattern is used to expose a part of the material layer such that the exposed part of the material layer is removed by an etching process using the photoresist layer pattern as an etching mask. In this way, a material layer pattern, corresponding to the light shielding pattern of the photo mask, can be formed.
In the implementation of such a photolithography process, impurities on the photo mask may be transcribed onto the photoresist layer, thus making it impossible to achieve the photoresist layer pattern having a desired profile. Consequently, an unwanted pattern is possibly formed on the material layer. Moreover, if some of the impurities on the photo mask have a size exceeding a critical value, a haze, which is known as a growing defect having a gradually increasing size, may occur. Haze is a main reason for defective pattern transcription.
For this reason, a conventional method for fabricating a photo mask comprises a cleaning process for removing impurities caused during a patterning process. The cleaning process may be selected from among SPM (sulfuric acid peroxide mixture) cleaning, APM (ammonia peroxide mixture) cleaning, ultra-pure water cleaning processes, etc. The SPM cleaning process is for cleaning a photo mask at a predetermined temperature by use of a mixture of sulfuric acid and hydrogen peroxide. Due to the use of sulfuric acid, in this case, sulfate may remain on the photo mask. The APM cleaning process is for cleaning a photo mask at a predetermined temperature by use of a mixture of a very small amount of ammonia, hydrogen peroxide, and ultra-pure water. In this case, ammonia may remain on the photo mask. When occasion demands, rather than being directly formed on the surface of the photo mask, the above mentioned residues may first diffuse into a transparent substrate, a light shielding layer, and a phase shift layer, which constitute the photo mask, and then, erupt from the surface of the photo mask. Although the above described cleaning processes respectively remove the impurities on the surface of the photo mask, the cleaning processes may adversely result in residual ions causing haze.
The residual ions, caused by the cleaning processes, tend to react with any peripheral, highly reactive materials upon receiving light energy during an exposure process. If the size of the residual ions exceeds a critical value, haze occurs. As described above, the haze causes undesired pattern transcription.